Of all his virtues, St. Joseph is most well known for his purity of heart. This can be seen in many different ways.
Certainly Joseph was pure of heart because he was chaste. By being chaste, Joseph was able to love with an upright and undivided heart.
Yet purity of heart is more than just chastity. It also involves charity and a love of the truth. Joseph also had purity of intention, seeking to do God’s will in everything, which means he avoided doing good deeds to be seen by others and did them for the love of God.
Joseph also was pure of heart because he had purity of vision. He disciplined his internal and external sight, his feelings and imagination, so as in no way to agree to impure thoughts, be they sexual or against charity or humility.
Most importantly St. Joseph was pure of heart because he was a man of prayer. Not only did he understand as St. Augustine wrote, that one can not be chaste without the help of God, but he understood as Saint Francis did, that purity of heart means despising the things of the earth and seeking heavenly things so that one might continually see and adore the Lord God living and true.